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Measurement of the time-integrated $CP$ asymmetry in $D^0 \to K^0_S K^0_S$ decays

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Abstract

The time-integrated $CP$ asymmetry in the decay $D^0 \to K^0_S K^0_S$ is measured using $3 fb^{-1}$ of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The flavour of the $D^0$ meson is determined by use of the decay $D^{*+} \to D^0 \pi^+$ and its charge conjugate mode. The result is \[ {\cal A}_{CP} = -0.029 \pm 0.052 \pm 0.022, \] where the first uncertainty is statistical and the second systematic. The result is consistent with Standard Model expectations and improves the uncertainty with respect to the only previous measurement of this quantity by more than a factor of three.

Figures and captions

Distribution of $\Delta m$ for the control channel $ D ^0 \rightarrow K ^- \pi ^+ $ in (left) linear and in (right) logarithmic scale. The solid (black) line corresponds to the total fit, the dashed (blue) line corresponds to the background, and the dash-dotted (red) line represents the signal contribution.

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Distributions of $\Delta m$ split into (left) $ D ^{*+}$ , (right) $ D ^{*-}$ and (top) LL , (bottom) LLtrig , including the fit function. The solid (black) line corresponds to the total fit, the dashed (blue) line corresponds to the background, and the dash-dotted (red) line represents the signal contribution.

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Distributions of $\Delta m$ split into (left) $ D ^{*+}$ , (right) $ D ^{*-}$ and (top) LD , (bottom) DD , including the fit function. The solid (black) line corresponds to the total fit, the dashed (blue) line corresponds to the background, while the dash-dotted (red) line represents the signal contribution.

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Animated gif made out of all figures.

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Tables and captions

Definition of candidate categories.

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Number of signal candidates and $ C P$ asymmetry obtained from the fits in the four categories.

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Supplementary Material [file]

Supplementary material full pdf

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supplementary.pdf

This ZIP file contains supplementary material for the publication LHCb-PAPER-2015-030. The files are: supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in various formats

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Created on 11 July 2020.